/* * jfdctflt.c * *該文件為前向DCT的浮點(diǎn)運(yùn)算，它要比整數(shù)運(yùn)算更精確。  *  */#ifdef DCT_FLOAT_SUPPORTED/*/*該程序只適用于8×8的塊變換*/	#if DCTSIZE != 8  Sorry, this code only copes with 8x8 DCTs. /* deliberate syntax err */#endif/* 在一個采樣塊上進(jìn)行DCT變換 */GLOBAL(void)jpeg_fdct_float (FAST_FLOAT * data){  FAST_FLOAT tmp0, tmp1, tmp2, tmp3, tmp4, tmp5, tmp6, tmp7;  FAST_FLOAT tmp10, tmp11, tmp12, tmp13;  FAST_FLOAT z1, z2, z3, z4, z5, z11, z13;  FAST_FLOAT *dataptr;  int ctr;/* 第一部分，對行進(jìn)行計算 */  dataptr = data;  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {    tmp0 = dataptr[0] + dataptr[7];    tmp7 = dataptr[0] - dataptr[7];    tmp1 = dataptr[1] + dataptr[6];    tmp6 = dataptr[1] - dataptr[6];    tmp2 = dataptr[2] + dataptr[5];    tmp5 = dataptr[2] - dataptr[5];    tmp3 = dataptr[3] + dataptr[4];    tmp4 = dataptr[3] - dataptr[4];    /* 對偶數(shù)項進(jìn)行運(yùn)算 */        tmp10 = tmp0 + tmp3;	/* phase 2 */    tmp13 = tmp0 - tmp3;    tmp11 = tmp1 + tmp2;    tmp12 = tmp1 - tmp2;        dataptr[0] = tmp10 + tmp11; /* phase 3 */    dataptr[4] = tmp10 - tmp11;        z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */    dataptr[2] = tmp13 + z1;	/* phase 5 */    dataptr[6] = tmp13 - z1;    /* 對奇數(shù)項進(jìn)行計算 */    tmp10 = tmp4 + tmp5;	/* phase 2 */    tmp11 = tmp5 + tmp6;    tmp12 = tmp6 + tmp7;    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */    z11 = tmp7 + z3;		/* phase 5 */    z13 = tmp7 - z3;    dataptr[5] = z13 + z2;	/* phase 6 */    dataptr[3] = z13 - z2;    dataptr[1] = z11 + z4;    dataptr[7] = z11 - z4;    dataptr += DCTSIZE;	/* 將指針指向下一行 */  }/* 第二部分，對列進(jìn)行計算 */  dataptr = data;  for (ctr = DCTSIZE-1; ctr >= 0; ctr--) {    tmp0 = dataptr[DCTSIZE*0] + dataptr[DCTSIZE*7];    tmp7 = dataptr[DCTSIZE*0] - dataptr[DCTSIZE*7];    tmp1 = dataptr[DCTSIZE*1] + dataptr[DCTSIZE*6];    tmp6 = dataptr[DCTSIZE*1] - dataptr[DCTSIZE*6];    tmp2 = dataptr[DCTSIZE*2] + dataptr[DCTSIZE*5];    tmp5 = dataptr[DCTSIZE*2] - dataptr[DCTSIZE*5];    tmp3 = dataptr[DCTSIZE*3] + dataptr[DCTSIZE*4];    tmp4 = dataptr[DCTSIZE*3] - dataptr[DCTSIZE*4];    /* 對偶數(shù)項進(jìn)行運(yùn)算 */        tmp10 = tmp0 + tmp3;	/* phase 2 */    tmp13 = tmp0 - tmp3;    tmp11 = tmp1 + tmp2;    tmp12 = tmp1 - tmp2;        dataptr[DCTSIZE*0] = tmp10 + tmp11; /* phase 3 */    dataptr[DCTSIZE*4] = tmp10 - tmp11;        z1 = (tmp12 + tmp13) * ((FAST_FLOAT) 0.707106781); /* c4 */    dataptr[DCTSIZE*2] = tmp13 + z1; /* phase 5 */    dataptr[DCTSIZE*6] = tmp13 - z1;    /* 對奇數(shù)項進(jìn)行計算 */    tmp10 = tmp4 + tmp5;	/* phase 2 */    tmp11 = tmp5 + tmp6;    tmp12 = tmp6 + tmp7;    z5 = (tmp10 - tmp12) * ((FAST_FLOAT) 0.382683433); /* c6 */    z2 = ((FAST_FLOAT) 0.541196100) * tmp10 + z5; /* c2-c6 */    z4 = ((FAST_FLOAT) 1.306562965) * tmp12 + z5; /* c2+c6 */    z3 = tmp11 * ((FAST_FLOAT) 0.707106781); /* c4 */    z11 = tmp7 + z3;		/* phase 5 */    z13 = tmp7 - z3;    dataptr[DCTSIZE*5] = z13 + z2; /* phase 6 */    dataptr[DCTSIZE*3] = z13 - z2;    dataptr[DCTSIZE*1] = z11 + z4;    dataptr[DCTSIZE*7] = z11 - z4;    dataptr++;			/* 將指針指向下一列 */}#endif /* DCT_FLOAT_SUPPORTED */